ABSTRACTMIGRATION OF ANTIOXIDANTS FROM POLY(LACTIC ACID), PLA, FILMS INTO FOOD SIMULANTS: A PARAMETER ESTIMATION APPROACHByHayati SamsudinDevelopment of antioxidant active packaging has vastly increased over the years with more focus on biodegradable polymeric films and natural antioxidants. However, few studies investigated the migration of antioxidants from films into food simulants/products by fully considering the kinetic migration parameters. To the best of the author’s knowledge, a selective number of studies have simultaneously determined other migration parameters besides the diffusion coefficient (D), such as the convective mass transfer coefficient (h) and the partition coefficient (Kp,f). Thus, this dissertation explored experimental and theoretical approaches to gain insight on the migration kinetics of antioxidants from polymer films by using parameter estimation approaches (e.g., ordinary least square (OLS), sequential, bootstrap etc). A poly(lactic acid), PLA, functional film incorporated with marigold flower extract containing carotenoid-based antioxidant (i.e., astaxanthin) was developed and the kinetic release of astaxanthin from this film into 95% ethanol was investigated. The mass migrated at equilibrium (M∞) was estimated for the first time, in addition to the D. Further investigation was conducted on different migration case studies to compare the estimation of one parameter, 1P (i.e., the D) versus 2P (i.e., the D and the M∞) and 3P (i.e., the D, the M∞ and the ratio of the mass of antioxidant migrated into the simulant to the mass of the antioxidant left in the film at equilibrium (α)) using general mass transfer solutions. The 3P estimation based on the corrected Akaike information criterion (AICc) was found to better describe the migration experiment without compromising the estimation accuracy. The α parameter, experimentally determined at the end of the experiment and related to Kp,f by α=V_f/(K_(p,f) V_p ), was better estimated at early times without the need to reach equilibrium; however, these migration cases did not account for the convective mass transfer coefficient.Hence, a two-step solution was developed to simultaneously assess the D, Kp,f, and h from migration experiments. The first step of the solution was to identify the right local minima region for minimizing sums of squared errors (SSE) and to provide a robust magnitude approximation for the initial guesses used in the second step of the OLS estimation. The Kp,f parameter was directly used in this solution due to the ease of physical interpretation. h, the parameter that might be of importance in a non-stirring condition, viscous food product/simulant, etc. was also estimated and related to the overall migration resistance (Bi=(hL)/D). Commonly, h is not estimated. Neglecting h might lead to underestimation of D, thus compromising the accuracy of the parameter estimation. Different migration case studies were used as examples and the parameters were assessed using the two-step solution. The OLS results were found comparable with the sequential estimation. Residual bootstrap was conducted to improve the residual distribution in a large population. A comparative study between the two-step solution and the general mass transfer solutions available in the literature was also performed, and model selection was performed using the AICc. A decision tree analysis consisting of the newly proposed model with the general mass transfer solutions was proposed as a tool for analyzing migration data. Finally, the estimation of the activation energy (Ea) of a non-isothermal migration study was conducted using the reparameterized Arrhenius equation to identify the optimum Tref to obtain near zero correlation between the Dref and the Ea, in turn, decreasing relative error of Dref.
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